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1.
Small and wide-angle X-ray scattering experiments with in-situ deformation of dry flax fibres have been carried out. An increase in the (200) peak intensity during deformation has been attributed to strain-induced crystallisation of the cellulose microfibrils, and provides evidence that the non-crystalline cellulose chains are initially oriented. However, no change in the equatorial small-angle streak (from cellulose microfibrils), the meridional reflection (from a crystalline/non-crystalline repeat along the fibre), or the microfibril orientation was seen. 相似文献
2.
P. Gamallo R. J. Astley 《International journal for numerical methods in engineering》2006,65(3):425-444
A novel numerical method is proposed for modelling time‐harmonic acoustic propagation of short wavelength disturbances on non‐uniform potential flows. The method is based on the partition of unity finite element method in which a local basis of discrete plane waves is used to enrich the conventional finite element approximation space. The basis functions are local solutions of the governing equations. They are able to represent accurately the highly oscillatory behaviour of the solution within each element while taking into account the convective effect of the flow and the spatial variation in local sound speed when the flow is non‐uniform. Many wavelengths can be included within a single element leading to ultra‐sparse meshes. Results presented in this article will demonstrate that accurate solutions can be obtained in this way for a greatly reduced number of degrees of freedom when compared to conventional element or grid‐based schemes. Numerical results for lined uniform two‐dimensional ducts and for non‐uniform axisymmetric ducts are presented to indicate the accuracy and performance which can be achieved. Numerical studies indicate that the ‘pollution’ effect associated with cumulative dispersion error in conventional finite element schemes is largely eliminated. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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4.
Demet Korucu Ercan Ertekin İbrahim Belenli Semsettin Altindal 《Journal of Superconductivity and Novel Magnetism》2013,26(6):2165-2170
The dielectric loss (ε″) properties of MgB2 composites were investigated by using the conductance–voltage (G/w–V) measurements in the wide frequency and applied bias voltage range at four different temperature levels. Experimental results show that both G/w and ε″ are found strong functions of frequency and applied bias voltage for each temperature level. These changes in G/w and ε″ are considerably high especially at low frequencies and temperatures. The values of ε″ decrease exponentially with increasing frequency until 100 kHz and then become almost constant. Such behavior of G/w and ε″ shows that interfacial polarization is more effective especially at low frequencies. In addition, the current–voltage (I–V) characteristics were also evaluated for 100, 200, and 300 K, and the I–V curves for each temperature show linear behavior. Results indicate that the G/w–V measurements may be a useful tool to characterize the dielectric properties and conductivity of MgB2. 相似文献
5.
The adsorption of Th4+ ions was studied on composites of polyacrylamide (PAAm) with montmorillonite (Mt), clinoptilolite (Z) and zeolite Y (ZY), and after phytic acid (Phy) modification.The monolayer adsorption capacity was 0.33 and 0.65 mol kg? 1 for PAAm-Mt and PAAm-Mt-Phy, 0.07, 0.21 and 0.60 mol kg? 1 for Z, PAAm-Z and PAAm-Z-Phy, and 0.74, 0.89 and 1.18 mol kg? 1 for ZY, PAAm-ZY and PAAm-ZY-Phy. The enthalpy and entropy changes were positive for all adsorbents. The adsorption kinetics followed the pseudo-second order model indicating that the rate controlling step was chemical adsorption by ion exchange. The reusability tests for five uses proved that the PAAm-Mt and PAAm-Z were reusable and complete recovery of the adsorbed ions was possible. ZY and the composites modified with Phy were not reusable. The presence of foreign metal cations did not influence the Th4+ adsorption. The adsorbed Th4+ onto the columns was effectively recovered with diluted HNO3. 相似文献
6.
We present two fully sequential indifference-zone procedures to select the best system from a number of competing simulated systems when best is defined in terms of the maximum or minimum expected performance. These two procedures have parabola shaped continuation regions rather than the triangular continuation regions employed in several papers in the existing literature. The procedures we present accommodate unequal and unknown variances across systems and the use of common random numbers. However, we assume that basic observations are independent and identically normally distributed. We compare the performance of our procedures with those of other fully sequential procedures available in the literature. 相似文献
7.
R. J. Astley J.‐P. Coyette 《International journal for numerical methods in engineering》2001,52(12):1379-1396
A number of spheroidal and ellipsoidal infinite elements have been proposed for the solution of unbounded wave problems in the frequency domain, i.e solutions of the Helmholtz equation. These elements are widely believed to be more effective than conventional spherical infinite elements in cases where the radiating or scattering object is slender or flat and can therefore be closely enclosed by a spheroidal or an ellipsoidal surface. The validity of this statement is investigated in the current article. The radial order which is required for an accurate solution is shown to depend strongly not only upon the type of element that is used, but also on the aspect ratio of the bounding spheroid and the non‐dimensional wave number. The nature of this dependence can partially be explained by comparing the non‐oscillatory component of simple source solutions to the terms available in the trial solution of spheroidal elements. Numerical studies are also presented to demonstrate the rates at which convergence can be achieved, in practice, by unconjugated‐(‘Burnett’) and conjugated (‘Astley‐Leis’)‐type elements. It will be shown that neither formulation is entirely satisfactory at high frequencies and high aspect ratios. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
8.
9.
Determination of photoinitiated polymerization of multifunctional acrylates with acetic acid derivatives of thioxanthone by RT-FTIR 总被引:1,自引:0,他引:1
Feyza Karasu Meral AydinM. Arif Kaya Demet Karaca BaltaNergis Arsu 《Progress in Organic Coatings》2009
Photopolymerization of multifunctional acrylates with 2-thioxanthone-thioacetic acid (TXSCH2COOH) and 2-(carboxymethoxy) thioxanthone (TXOCH2COOH) as the one-component photoinitiator has been investigated by real-time Fourier transform infrared (RT-FTIR) spectroscopy. The photobleaching of these one-component nature initiators was performed in air. The irradiation time for total bleaching was 240 s for TXSCH2COOH and 540 s for TXOCH2COOH. 相似文献
10.
Smart structures and their applications on active vibration control: Studies in the Department of Aerospace Engineering, METU 总被引:1,自引:0,他引:1
Melin Sahin Fatih Mutlu Karadal Yavuz Yaman Omer Faruk Kircali Volkan Nalbantoglu Fatma Demet Ulker Tarkan Caliskan 《Journal of Electroceramics》2008,20(3-4):167-174
This work presents the theoretical and experimental studies conducted in Aerospace Engineering Department of Middle East Technical
University on smart structures with particular attention given to the structural modelling characteristics and active suppression
of in-vacuo vibrations. The smart structures considered in these analyses are finite and flat aluminium cantilever beam-like
(called as smart beam) and plate-like (called as smart fin) structures with surface bonded lead–zirconate–titanate patches.
Finite element models of smart beam and smart fin are obtained. Then the experimental studies regarding open loop behaviour
of the structures are performed by using strain gauges and laser displacement sensor to determine the system models. Further
studies are carried out to obtain H
∞ and μ-synthesis controllers which are intended to be used in the suppression of free and forced vibrations of the smart structures.
It is observed that satisfactory attenuation levels are achieved and robust performance of the systems in the presence of
uncertainties is ensured. In that respect a comparative study involving H
∞ and sliding mode controls is also conducted. Recently, the studies involving aerodynamic loading are also gathering pace. 相似文献